ZITO (ZnO-SnO 2 -In 2 O 3 ) Transparent Conducting Oxides: Electrical and Optical Properties of DC Magnetron Sputtered F
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0905-DD01-07.1
ZITO (ZnO-SnO2 -In2 O3 ) Transparent Conducting Oxides: Electrical and Optical Properties of DC Magnetron Sputtered Films Cleva W. Ow-Yang1 , Hyo-Young Yeom2 , Burag Yaglioglu2 , and David C. Paine2 1 Sabanci University, Faculty of Engineering & Natural Sciences, Orhanli, Tuzla, 34956 Istanbul, Turkey 2 Brown University, Division of Engineering, Box D, Providence, Rhode Island 02912, USA ABSTRACT Amorphous ZITO films were deposited by dc magnetron sputtering onto glass substrates from ceramic oxide targets containing Zn:In:Sn cation ratios of 1:2:1 and 1:2:1.5. The microstructure, carrier density, mobility, and resistivity of as-deposited and annealed samples were evaluated using x-ray diffraction and Hall effect measurements. The as-deposited films were amorphous and remained so after annealing at 200°C in air for up to five hours. Transmissivity of the films exceeded 80% in the visible spectral region. The minimum -4 resistivity value (7.6x10 Ω-cm) was obtained from thin films deposited using the 1:2:1 composition target and a substrate temperature of 300ºC. INTRODUCTION Transparent conductive oxide (TCO) thin films are widely used as IR reflectors and as electrodes in display applications that require both optical transparency and electrical contact. Indium oxide films doped with tin (ITO) or zinc (IZO) are used in high value applications that require near-metal-like resistivity (1-2x10-4 Ω-cm) and 80-90% transmissivity to visible light. The high cost of indium metal has led to increased interest in, and active pursuit of, alternative transparent conducting oxide materials that use less scarce and lower cost materials. In this report we describe our efforts to displace In metal in ITO with Zn. Tin-doped and pure indium oxide deposited by DC magnetron sputter deposition onto unheated substrates is found to be amorphous under a wide range of total Ar sputter pressure and sputter system design parameters [1]. These amorphous materials are known to undergo crystallization at measurable rates at temperatures as low as 120ºC [2]. In contrast, amorphous IZO (indium oxide with ~10 wt% ZnO) remains amorphous [3],[4] for up to an hour during heating at 500°C in air. The stabilization of the amorphous indium oxide phase by Zn is most likely due to the 4-fold coordination of Zn2+and is incompatible with the bixbyite In2 O3 phase, which is based on the stacking of two closely related 6-fold coordination units. The very limited solid solubility of Zn in indium oxide and the absence of Zn-In-O compounds in the In-rich side of the phase diagram [5] suggests that the a/c-transformation in IZO would require phase separation via cation diffusion. In any case, it is well established [6] ,[7],[8] that neither Sn nor Zn are electrically active dopants in amorphous indium oxide and that the largest source of carriers in a-IZO and a-ITO are oxygen vacancy-like defects. The stabilization of the amorphous indium oxide phase with ZnO offers the possibility of exceeding the 10 wt% solubility limit of SnO 2 in crystalline bix
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